(1) Field of the Invention
The present invention relates to the crushing or digesting of used fluorescent tubes and separating the components. More particularly the present invention relates to an improved arrangement for separating the metallic electrical tips originally capping the ends of the tubes from the fractured glass of the fluorescent tubes. More particularly, the present invention relates to an improved shape and arrangement for a so-called bar screen, or grizzly, for separating and handling metal tips and fractured glass from crushed fluorescent light tubes in a fluorescent light digestion or recycling and disposal apparatus.
(2) Discussion of the Prior Art
Fluorescent light-tubes are formed from elongated, cylindrical or tubular glass receptacles which are charged with mercury or other conductive vapors. The inside surface of the tube is coated with a fluorescent coating of some form such as phosphorus itself or other phosphor powders such as antimony, beryllium, cadmium and strontium compounds plus in some cases, lead and the like. Mercury vapor as well as beryllium, strontium, lead and cadmium are well known as potentially toxic materials as are other phosphor powders with which the inside of the fluorescent tube may be coated. Older fluorescent tubes often use high concentrations of beryllium powders, but this has been in general superseded in more recent fluorescent tubes by cadmium-type powder.
Since fluorescent tubes are, in general, bulky and unsatisfactory for disposal without treatment, it has become customary to crush them into small pieces by various means and then dispose of the fractured pieces. Merely fracturing the tube itself into small pieces for disposal, however, is not very satisfactory because of the potentially toxic nature of the dust and vapor originally confined inside the fluorescent tube. Such potentially toxic particulates, which occur mostly in the form of small dust particles plus mercury vapor and small drops or beads of mercury, can be quite detrimental if they escape to the environment.
In previous applications filed by the present Applicant, methods and means for crushing fluorescent tubes and then separating the fractured glass particulates from the potentially toxic materials contained within the original tube have been disclosed. Such methods and apparatus are based on an air separation effected between the glass particulates and the smaller toxic powders and vapors contained within the original fluorescent tubes. In particular, in accordance with such previous inventions, the fractured fluorescent tube materials are exposed to a rapidly moving body of gas such as stripping air, preferably passing countercurrently with such particulates. In this way the smaller, lighter dust and mercury vapor is carried away to a recovery system while the glass particulates are removed from the system for recycling to glass manufacturers and the like. In order to provide such separation, it is important that the glass particulates not be crushed too small so that they will have sufficient-weight such that they will not be carried away by the stripping gas together with the small toxic powder particles.
In Applicant's U.S. application Ser. No. 458,177 filed Dec. 28, 1989,now U.S. Pat. No. 5,092,527, a flat, rapidly rotating blade was disclosed for fracturing fluorescent tubes thrust down a feed chute into the path of the rotating blade. The blade, upon striking the fluorescent tube, fractured such tube into small particles and these were then conveyed by gravity and other means through a system while separating toxic powder from the surfaces both by gravity processes and particularly by countercurrent air flow or gas stripping processes. As indicated above, it is important in crushing the glass that the pieces not be too small such that they may be carried away with countercurrent stripping air, nor should such pieces of glass be too large or they will not only not pack efficiently, but will also not have an effective configuration for passage therethrough of stripping air for stripping away of the toxic powder normally adhering to the original inside surface of the fluorescent tube. Consequently, it is highly desirable for the fractured glass particulates to be of fairly uniform size and shape.
It is also not only desirable, but necessary for the electrical tips provided upon the ends of the fluorescent tubes to be removed from the fractured glass at some point, since otherwise the glass would not be readily recyclable for remelting and reuse. It is also desirable that the glass be removed cleanly from the tips with as little damage to the tip as possible since any remaining glass would interfere with recycling of metal components of the tips.
In a concurrently filed application by the same inventor, a novel fracturing or crushing blade for fluorescent tube crushers is disclosed such blade comprising essentially a rotatable blade having a flat or blunt fracture blade section from the upper portion of which there extends forwardly a relatively sharp striking blade which upon striking the tip, does minimum damage to the tip itself and upon striking the glass portion of the fluorescent tube, effects a particularly uniform fracture of the glass into relatively uniform size pieces of glass and also effects a rather clean separation of the glass from the electrical tip. The fractured glass and the tips are then passed into and through a countercurrent gas flow stripping chamber where the potentially toxic powder and metal vapors from the inside of the tube are carried upwardly away from the fractured glass particulates which fall through the countercurrent gas stripping chamber preferably being impacted several times within such chamber upon baffles which jar the fractured glass particulates and aid in detaching adherent phosphors from the surface. In accordance with a still further application of the present Applicant, the fractured glass particulates are then passed through a mixing and abrading apparatus where the fractured glass particulates are moved past each other in surface contact rubbing off residual or remaining potentially toxic phosphors and/or other powders. The fractured glass particulates passed through the mixing and abrading apparatus, which may take various forms including spiral mixing auger means, rotating cylindrical mixing apparatus, fluosolids means and the like, but preferably, at the present time, the form of a rotating auger means, are exposed again to a countercurrent stripping gas stream either concurrently with the mixing and abrading operation or subsequent thereto for removal of any toxic phosphor powders detached from the surface of the fractured glass particulates during such operation. The stripping gas from the stripping operations is then passed to a particle removal apparatus including preferably cyclone separators, bag house-type separators and one or more filters and absorbers. The fractured glass particulates during treatment subsequent to the original fracture step are desirably not further fractured, but maintained in their original fractured size range so that their size does not decrease to a point where they are likely to be stripped away with the potentially toxic powder.
As indicated above, it is necessary to remove the broken-off tips from the fractured glass particulates somewhere in the operation prior to removal of the fractured glass from the operation. Such tip removal can be accomplished at several points in the process, including immediately subsequent to the fracturing stage, subsequent to the first countercurrent stripping operation and subsequent to the second countercurrent stripping either during or subsequent to the mixing and abrading step. It has been found that with the new and improved fracture blade disclosed and claimed in the concurrently filed application, that the breaking away of the glass from the tips is essentially complete. Consequently, there is no reason to conduct the tips through the mixing and abrading operation where the tips may become damaged in any event. It has been found convenient, therefore, to remove the tips from the tube digestion operation at the conclusion of the initial countercurrent stripping and jarring operation, although other locations in the process are also possible.
Applicant originally used a vibrating screen to, in effect, screen out the tips from the fractured glass particulates. Bar-type sieving apparatus was then adopted. However, difficulty has been encountered in the use of screen-type apparatus, particularly with the filament elements of the tips becoming wrapped around the screen material in effect tying the tip to the screen and ultimately occluding the whole screen. The use of a conventional bar sieve or grizzly has also been found to not be effective. Difficulty with tangling of the electrode wires about the apparatus has been encountered and the usual trapezoidal shape of the bars has been found to interfere with effective removal of the flat glass sections through the bars.
The operation of screening out large solid particulates from smaller solid particulates or particles is an old art which may be broadly separated into four main categories of apparatus (a) grizzlies, (b) shaking screens (c) vibrating screens and (d) oscillating screens. Grizzlies and shaking screens are frequently used for larger separations of perhaps more than one inch. Oscillating and vibrating screens are customarily used for smaller separations such as in the range of 4 to 325 mesh size.
A grizzly comprises, from a technical standpoint, a set of parallel bars held apart by spacers of some form at a uniform distance. The bars are frequently made of some wear-resistant material such as manganese steel or the like. The bars are frequently in the form of a truncated downwardly oriented triangle, or trapezoid, to reduce plugging. The bars are also frequently inclined toward one end to facilitate movement of material across the surface of the grizzly. In one type of grizzly known as the self-cleaning-type, metal arms rotate between the bars to keep the spaces between open. So-called moving bar grizzlies are pivoted at one end and mounted against an eccentric shaft on the other with the eccentric at 180.degree. apart on adjacent bars. Oscillating grizzlies and vibrating grizzlies are also known.
The present Applicant, as noted above, found conventional grizzlies and screens to be usable to separate the tips from the fractured glass particulates, but the operation was not fully satisfactory. The tips not only tended to become stuck to the equipment, but also frequently carried glass with them out of the apparatus. There has been a need, therefore, in the separation of electrical tips from fractured glass particulates during the digestion of used fluorescent light tubes for an apparatus that will not only effectively separate the tips, but will also separate the glass from such tips.